Abstract. One distinctive characteristic of object-oriented data models over traditional database systems is that they provide more expressive power in schema definition. Nevertheless, the defining power of objectoriented models is still somewhat limited, mainly because it is commonly accepted that part of the semantics of the application can be represented within methods. The research work reported in this paper explores the possibility of enhancing the power of object-oriented data models in schema definition, thus offering more possibilities to reason about the intension of the database and better supporting data management. We demonstrate our approach by presenting a new data model, called CVL, that extends the usual object-oriented data models with several aspects, including view definition, recursive structure modeling, navigation of the schema through forward and backward traversal of links (attributes and relations), subsetting of attributes, and cardinality ratio constraints on links. CVL is equipped with sound, complete, and terminating inference procedures, that allow various forms of reasoning to be carried out on the intensional level of the database.
IntroductionOne distinctive characteristic of object-oriented data models over traditional database systems is that they provide more expressive power in schema definition. Indeed, several modeling constructs of object-oriented data models are borrowed from the research on semantic data modeling and semantic networks in Artificial Intelligence, and are intended to overcome well-known limitations of flat data representation. Nevertheless, the defining power of object-oriented models is still somewhat limited. Examples of useful representation mechanisms that are considered important especially for new applications, but are generally not considered in object-oriented schemas are: recursive class definitions, view definitions, cardinality ratio constraints on attributes, subsetting of attributes, inverse of attributes, union and complement of classes (see for example [9]). One reason for limiting the expressivity of schemas is that object-oriented models support method definitions, and it is generally accepted that some of the semantics of the application could be very well represented within methods.The research work reported in this paper explores the possibility of enhancing the power of object-oriented data models in schema definition. We argue that such enhancement is interesting from different points of view:-Capturing more semantics at the schema level allows the designer to declaratively represent relevant knowledge about the classes of the application. It follows that sophisticated types of constraints can be asserted in the schema, rather than embedding them in methods, with the advantage of devising general integrity checking methods to be included in future database systems. -Expressing more knowledge at the schema level implies more possibilities to reason about the intension of the database. Such reasoning can be exploited for deriving usefu...